Californians will go to the polls today knowing that their votes for the presidential election will be virtually worthless. President Obama has a double-digit lead over Mitt Romney in this bluest of states, and by the time polls close in California, the presidential race may very well have been decided.

But that doesn’t mean there aren’t other issues at stake in the Golden State. As they often do, Californians will also be voting on a number of ballot initiatives. And none are more important — or have gathered more attention and campaign money — than the one known as California Proposition 37. If approved, Prop 37 would mandate labels on “raw or processed food offered for sale to consumers if the food is made from plants or animals with genetic material changed in specified ways.” It would also prohibit any food with genetically modified (GM) ingredients from being labeled as “natural.”

Given that some 85% of the corn crop — which in turn is found in much of the food available at the average supermarket — is genetically modified, passage of Prop 37 would likely mean big changes for labeling and potentially for the American food system as well. In an article for the New York Times Magazine, the writer Michael Pollan argued that passage of Prop 37 would “change the politics of food not just in California but nationally too,” proving that the foodies could exert real political as well as economic power. Meanwhile, Big Ag companies like Monsanto are proving just how important stopping Prop 37 is to them by pouring tens of millions of dollars into a campaign to defeat the initiative.

Right now it looks like Big Ag has the edge — recent polls indicate that a narrow majority of Californians are poised to reject Prop 37. That’s a shift from earlier in the year, when polls showed that Prop 37 had strong support in the state. The vast fundraising edge belonging to the anti-initiative forces — which also includes companies like DuPont and PepsiCo — is almost certainly the driving factor behind that change, a fact that only confirms suspicions among many progressives that Big Ag wants to keep consumers in the dark over the GM ingredients in their food. They do — ag and biotech companies know there’s a deep suspicion among many consumers toward GM crops, a suspicion that supporters of Prop 37 have just as eagerly exploited. But the battle over Prop 37 and GM food was never really about science or health. It’s about politics — and who should control the U.S. food system.

Food is the most personal of environmental issues — after all, we vote on it three times a day — which is why GM food is so controversial. Head over to the home page of the Right to Know campaign backing Prop 37, and you’ll see item after item about the potential dangers of GM food. It’s “Frankenfood,” the potentially dangerous product of loosely regulated genetic engineering. A widely publicized French study that was published earlier this fall crystallized those fears — the scientists reported that they found that rats fed a lifetime diet of GM corn developed tumors and suffered organ damage compared with rats fed a non-GM diet.

But here’s the thing: mainstream scientists say there is little evidence that there are any harmful health effects associated with consuming GM crops. The National Academy of Sciences, the British Royal Academy, the World Health Organization, the American Medical Association and many other major scientific bodies have said publicly that GM food is not dangerous. Americans have been eating food made from GM crops for years and no one has yet been able to demonstrate a single case of someone actually getting sick from it. (See Keith Kloor’s piece on Slateon the scientific view of GM crops.) The board of the American Association for the Advancement of Science (AAAS) released a letter last month recommending against the special labeling of GM food and quoted from a recent E.U. report on GM crops:

The main conclusion to be drawn from the efforts of more than 130 research projects, covering a period of more than 25 years of research and involving more than 500 independent research groups, is that biotechnology, and in particular GMOs, are not per se more risky than e.g. conventional plant breeding.

Skeptics of GM food can and do argue that those studies may be flawed, that the biotech and ag industries keep tight control over GM research and that there are scientists who dissent from the mainstream view that GM crops aren’t dangerous. Some of that may be true — academic scientists have often expressed frustration that corporate patent rights over GM seeds limit researchers ability to freely study them. And there are definitely scientists who are much more skeptical toward GM food than many of their colleagues; molecular biologist Patricia Hunt and 20 other researchers signed a letter recently challenging that AAAS statement on Prop 37, arguing that the group’s position “tramples the rights of consumers to make informed choices.”

But there’s no getting around the fact that the majority of the science done so far indicates that GM food poses no known threat to consumers. That puts those warning about the threat of GM food in a very similar position to global-warming skeptics — defying the mainstream scientific consensus, calling into question the quality of the studies that form that consensus and seeking out dissenters who share their doubts. Environmentalism is supposed to be science-based, but the anti-GM-food forces have too often been antiscience.

Does that mean Californians should vote against Prop 37? Not necessarily. For one thing, the anti-initiative forces have also played fast and loose with the facts on some misleading advertisements. The argument made by opponents that Prop 37’s passage would cost consumers an extra $400 a year in grocery bills seems to assume that foodmakers would need to replace much of their stock rather than simply relabeling it. And even if the bulk of the science indicates that GM food poses no health threat, why shouldn’t it be easier for consumers who want to avoid GM ingredients to do so? The labels may not even make a huge difference — that’s the argument put forward by David Roepik, a risk expert, who wonders whether the labels might actually help speed the acceptance of GM foods by making them seem more normal.

Ultimately, though, Prop 37 isn’t really a battle over science — it’s a battle over the politics of food, as Michael Specter of the New Yorker writes:

Here’s what the hysteria is really about: corporate control of seeds. There is a feeling, expressed often and with great emotion, that this kind of commodity should not be hawked like software — with annual upgrades you have to buy. Normally, farmers save seeds for the coming season; but G.E. seeds usually only last for one planting. That scares farmers, understandably so — but it is not an issue that will be addressed by this labelling initiative. Monsanto doesn’t own the science — nor is science the only thing that matters. If people are unhappy with patent laws they can change them. If they have problems with the morality of an international conglomerate controlling the food we eat, then let’s elect people who want to make that more difficult. There are many people working on genetically engineered products that will help sustain people and the environment.

As Specter notes, the labeling initiative on Prop 37 won’t do much to change corporate control over the food system. In fact, if the initiative passes, it’s likely to be fought in the courts and may simply lead to more confusion. (That’s why the liberal political blogger Kevin Drum at Mother Jones wrote recently that he was opposed to Prop 37.) But even though I’m not really worried about GM crops (I think both the proponents and opponents of genetically engineered crops tend to overstate their cases), I can see why a Californian who wants to change how food is made in the U.S. would support Prop 37. “I’m on record saying that this shouldn’t be solved on the state level,” says Gary Hirshberg, founder of the ultra-organic Stonyfield Farm yogurt company and chairman of the Just Label It group, which supports greater federal regulation of GM crops. “But I still think there’s a clear choice to support Prop 37.”

Foodies get to exercise their franchise three times a day when it comes to buying and preparing more sustainable meals, but they rarely get a chance to vote on their convictions. Californians are doing so today — and we’ll see just how powerful the “dinner party” really is.